I think it's too much like Dishonored and Deus Ex. It isn't doing many things new and got bored pretty fast. Not even an hour into the game. It's also unclear sometimes what you have to do (chinatown...thinglevel).

I thought this game was awesome. I finished it over the weekend. Just a few comments to the OP.
1. play it a little longer before tossing the game aside. The first 3 hours are more of tutorials to show the different ways you can complete each level. (Guns blazing, sneaking, using uniforms, environmental kill, special kills, etc.)

2. A map is not necessary for the sand box levels. The trick is to sneak around and learn the environment and then decide how you want to take down your target. Instinct makes this possible.

3. Disguises work well if you use them in combination with instinct. When anyone suspects you, use your instinct and you cover your face so the person stops being suspicious.

4. Play a little more and the game will live up to it's name. There are lots of targets you need to take out in the game.

5. If you still don't like it, I understand. Everyone has different tastes. And I loved this game.

One question, does it have the sniper mini game? I remember seeing some of that in the build up and thought it looked fun.

No. I haven't, so I can't claim that this game is better, worse, different, etc. That's why my comments were solely based on my experience with this game only. But then again, I didn't play any Splinter Cell games either.

Is it a big departure?

Funny you say that, because I was very disappointed by Deus Ex: HR as well. Once again, I just could not see the stealth in it at all.

Dishonored is one of the few recent stealth games I have enjoyed.

An enormous departure, yes.

And Jay is right. It seems to me that people who have never really liked Hitman love Absolution whereas those who are fans of the series don't like it at all.

That's too bad. Maybe they should have not called it Hitman, then everyone would be happy.